A typical aerobic system consists of a trash tank, treatment unit (aeration chamber, air supply, clairifier), disinfection, pump tank, and spray field. Each component must perform it's intended purpose to acheive the desired effulent quality. Below is an interactive diagram of an aerobic treatment unit, click any component for details.
Aerobic treatment systems consist of several processes that work together to provide a high-quality effluent:
- Removal of grass solids (trash)
- Aeration
- Clairification
- Sludge return
Trash Tank
Wastewater leaves the house through a pipe and enters the trash tank. this is where the heavier solids will settle to the bottom while the lighter materials will float to the surface.
Potiental Issues:
- Tank integrity
- Lid integrity
- Failure of seals around risers, etc.
The wastewater flows from the trash tank into the aerobic treatment unit. Air is pumped into the aeration chamber of the unit, and the wastewater remains there for a relatively long period to allow the microbes to convert the waste into less harmful subtances: water, carbon dioxide, and new cells.
After the aeration process, the effluent now moves into a clarifier, which removes the microbial cells, cell waste, and dead cells from the wastewater. Clarifiers can be oriented vertically or horizontally.
Pump systems areused in many ways in On-site wasterwater treatment systems. For example, the may be used to store and deliver effluent to a spray field or other soil dispersal area.
Pump tanks may also be used earlier in the treatment train to deliver wastewater uphill to a treatment unit. In these applications, the tank may serve as a flow equalization tank.
The pump system consists of a pump tank, pump, discharge assembly, controller, and associated electrical components.
Aerobic treatment systems consist of several processes that work together to provide a high-quality effluent:
- Removal of grass solids (trash)
- Aeration
- Clairification
- Sludge return
Aerobic Systems rely on a continuous supply of oxygen to keep the microbes treating the wastewater heaalthy. Oxygen can be supplied to the wastewater in several ways, including by aerators, compressors and blowers.
Pump systems should include a controller to sense water level in the tank, and dose the field when required, or set off alarms if needed. The control panel can be simple or complex depending on the functions it must perform. Some examples of controller functions are:
- Automatically turning the pump on and off with a manual override.
- Sounding an alarm to indicate problems.
- Providing a means of monitoring the system (meters/counters).
- Electronic monitoring and automatic notifications
- Monitoring the air system and tracking air pressure levels to extend compressor's lifespan and ensure proper treatment.
The solids that settle in the clarifier should be returned to a previous component. Usually the seetled material, or sludge that settles is returned to the aeration chamber via a sloped tank bottom, or pump that returns the sludge to the aeration process.
Sludge return is essential to the treatment process. With sludge return, the microbes in the sludge breakdown additional wastewater and reproduce, increasing the population to replace dying microbes.
Chlorinators (Tablet & Liquid) and UV light systems serve as secondary treatment devices. Tablet Chlorinators are most common.
Tablet Chlorinators typically consist of a long narrow tube that holds tablets, which acts as a dispenser for the tablets into the effluent below.
- More info on chlorinators
Aerobic treatment units are pre-secondary treatment devices. They can remove substsntial amounts of BOD & TSS that are not eliminated by simple sedimintation. The aerobic process also breaks down dissolved solids and ammonia and reduces the number of pathogens in waste. These processes may occur either in separate chambers of a single tank or in a series of tanks.
Wastewater Treatment Processes
The aerobic treatment process involves two types of microbes living together:
- Aerobic microbes, which use free oxygen dissolved in wastewater
- Facultative microbes, which can grow in envrionments that have free oxygen and those that do not.
These two types of microorganisms can decompose a broad range of materials.
Conventional onsite wastewater treatment systems depend on the soil and the organisms in it to treat wastewater.
Step 2: Aeration Process
Aerobic Systems rely on a continuous supply of oxygen to keep the microbes treating the wastewater healthy. Oxygen can be supplied to the wastewater in several ways depending on the brand of system, but can include aerators, compressors or blowers.
Tracking air pressure can significantly effect the longevity of your system.
| High Air Pressure: | Low Air Pressure: |
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Step 3: Clarification
Potiental Issues:
- High water usage can cause a buildup of solids, either in top of the clarifier or deep in the chamber, leading to excessive solids being carried over into the pump tank.
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Vertical clarifiers: The wastewater enters through the bottom of the chamber, and flows upwards, toward the outlet.
Horizontal clarifiers: The wastewater flows laterally from the inlet to the outlet.
Active filtration: Another approach to clarification is active filtration. Some aerobic treatment unit products incorporate filtration media to filter the biomass from the effluent before it is discharged. In these approaches, the effluent filters through a porous material or settles in a plate-settling process. One type uses socks to filter the effluent leaving the aerobic chamber.
During the clarification process, some materials will float to the surface of the clarifier. These floating materials can be skimmed from the surface of the clarifier.
In all clarifiers, the waste particles must be able to settle to the bottom of the tank. For a particle to settle, the downward forces must be greater than the upward forces.
Several factors affect the settling process:
- Gravity pulls the material downward.
- The Density of the materials determines the rate at which it falls. This is because gravity pulls down the material at a speed based on the material's weight.
- Bouyancy pushes the materials upward. The water is resisting te object down through it and is actually pushing it up based on the amount of water being displaced.
- The speed of water flow in the system is a crucial factor in the design of a clarifier. Water flow carries suspended particles along with the water. When the water is moving to fast, fewer particles can settle to the bottom.
- Turbulence can also interfere with the down-ward movement of particles.
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Step 4: Sludge Return
The solids that settle from the effluent in the clarifier should be returned to a previous component. Usually, the settled material, or sludge from the clarifier, is returned to the treatment tank via a sloped clarifier bottom. Sludge return is essential to the treatment process. With sludge return, the microbes in the sludge breakdown additional wastewater and reproduce, increasing the population to replace dying microbes. Several systems use a compartmented tank to automattically feed the sludge back to the aeration chamber. In these systems, the rolling motion of the effluent in the aeration chamber will intrain the sludge back into the digestion process.
Other systems that use a seprate tank for a clarifier may have a pump to return solids, either to the trash or treatment tank. Additionally, returning the solids to the trash tank may help remove more nitrogen from the system.
Most vertical settling chambers have a passive return process. Solids/sludge pass through the bottom of the clarifier and return to the aeration process. Horizontal clarifiers typically have a seprate chamber where solids accumulate and require an active return process.
Step 5: Disinfection
Some pretreatment devices include a disinfection unit as part of the treatment system. In the disinfection process, disease-causing organisms are destroyed or inactivated. This process reduces the concetraction of pathogens to an acceptable level. However the wastewater is only disinfected, not steralized (free of all life). Before the wastewater enters the disinfection stage, it must be pretreated to remove signifacant amounts of organic matter and solids. if these are not removed first, they can impede the disinfection process. Chlorinators (Tablet/Liquid) and UV light systems serve as secondary treatment devices. Tablet Chlorinators are most common.
Step 6: Pump tank and Controls
Pump systems areused in many ways in On-site wasterwater treatment systems. For example, the may be used to store and deliver effluent to a spray field or other soil dispersal area.
The pump system consists of a pump tank, pump, discharge assembly, controller, and associated electrical components.
